The invention relates to a method for the embossing of at least one relief pattern of high resolution, particularly a phase hologram or a phase diffraction grating, into a thermoplastic information carrier, by means of a heatable embossing matrix in the form of a foil, which carries the relief pattern.
Storage of information in the form of relief patterns of high resolution, such as phase holograms, phase diffraction gratings and the like, is well known. In such a process, the relief pattern is embossed by means of pressure and heat into the thermoplastic carrier which, depending on its end purpose, may be in the form of a card, a band, a foil or a disk. The embossed relief patterns which, for example, contain video-information or validity information, can be read mechanically by means of optical devices.
In a well-known method for embossing phase holograms, a thermoplastic film and an embossing matrix in the form of an endless band which carries the hologram relief pattern, are jointly passed between two calender rollers. During its passage between the calendar rollers, one of which is heated, the thermoplastic film is heated to a suitable temperature and is subsequently separated from the hologram matrix. This method permits a relatively high speed of passage, but requires significant investment and is therefore not economical when only a limited number of copies of a specific relief pattern are to be embossed, or when the relief pattern must constantly be changed. Moreover, this method does not permit the embossing of high-quality relief patterns of high resolution into a thermoplastic material when the surface of the latter is coated with a metallic layer.
The object of the invention is to propose a method of the kind mentioned at the outset, which would permit economical embossing of limited quantities of relief patterns with a high resolution, into either uncoated or metallic-coated thermoplastic material.
The invention consists in pressing the embossing matrix onto the thermoplastic carrier by means of a punch, while the embossing matrix is heated by a current running through it, and then maintaining the embossing pressure acting on the information carrier until the embossed relief pattern has hardened.
An embossing device to perform the method comprises an embossing matrix consisting of at least one band-shaped electric conductor connected to a source of current impulses and fastened to a punch.